RESPIRATION AND ACIDOSIS 313 



place so that they cannot be forced out by pressure of the mercury. 

 Rubber bands may be used for this purpose but it is suggested that 

 elastic cords of fine wire spirals, applied in the same manner as 

 rubber bands, are stronger and more durable. 



After a determination has been finished, the levelling bulb is lowered 

 without opening the upper cock, and most of the mercury is withdrawn 

 from the pipette through c. The water solution from d is readmitted 

 and the levelling bulb being raised to position i, the water solution, 

 together with a little mercury, is forced out of the apparatus through a. 1 



Procedure. Drawing the blood. 2 About six or seven c.c. of venous blood 

 are aspirated into a centrifuge tube (see Fig. 101) which contains a little powdered 



FIG, 102. SEPARATORY FUNNEL USED IN SATURATING BLOOD PLASMA WITH CARBON 

 DIOXIDE. (Journal Biological Chemistry, 30, 289, 1917.) 



potassium oxalate and some paraffin oil. The tube is subjected to a minimum 

 of agitation after the blood is in it. The slight amount of agitation necessary 

 to assure mixture with the oxalate is accomplished by stirring with the inlet 

 tube, rather than by inverting or shaking. The tube and contents are then 

 centrifuged. 



Saturation of Plasma with Carbon Dioxide. After centrifugation about 

 3 c.c. of the plasma 3 are transferred to a 300 c.c. separatory funnel, arranged 

 as in Fig. 102, and the air within the funnel is displaced by either alveolar air 

 from the lungs of the operator or a 5.5 per cent carbon dioxide-air mixture 

 from a tank. In either case the gas mixture must be passed over moist glass 

 beads before it enters the funnel. 



When alveolar air is used the operator, without inspiring more deeply than 

 normal, expires as quickly and as completely as possible through the glass beads 



1 It is well to have a funnel draining into a special vessel to catch the water residues 

 and mercury overflow from a. A considerable amount of mercury is thus regained if 

 many analyses are run. It requires only straining through cloth or chamois skin to prepare 

 it for use again. 



2 For at least an hour before the blood is drawn the subject should avoid vigorous 

 muscular exertion as this, presumably because of the lactic acid formed lowers the bi- 

 carbonate of the blood. (Christiansen, Douglas & Haldane: /. Physiol., 48, 246, 1914; 

 Morawitz & Walker: Biochem. Zeit., 60, 395, 1914.) 



3 If it is desired to keep the plasma for the estimation of carbon dioxide at a later time 

 it should be transferred to a paraffined tube, covered with a layer of paraffin oil, stoppered 

 and kept cold; under which conditions it is claimed that, if sterile, it may be kept for over 

 a week without alteration of its carbon dioxide capacity. 



